Molecular sensors based on scattering spectroscopy of single gold nanoparticles can be improved three-fold by the use of gold nanoshells instead of solid gold nanoparticles. The particle plasmon resonance responds more sensitively to changes in the environment, the biological spectral window is accessible, and the scattering spectra show sharper resonances. In particular, we focus our discussion on the narrow homogeneous line width of only 180 meV.

Access to the full text of the published version may require a subscription. ‡ Electron Microscopy and Analysis Facility (EMAF), Tyndall National Institute, Lee Maltings, Prospect Row, Ireland. KEYWORDS (Word Style "BG_Keywords"). If you are submitting your paper to a journal that requires keywords, provide significant keywords to aid the reader in literature retrieval. Rights Supporting Information PlaceholderABSTRACT: Semiconductor nanowires have been the subject of intensive research investment over the past few decades. Their physical properties afford them applications in a vast network of active microelectronic research fields, including logic device scaling in very large scale integrated circuits, sensor devices and energy harvesting. A range of routes to semiconductor nanowire production have opened up due to advances in nanowire fabrication techniques over the last number of decades. These nanowire fabrication routes can usually be categorized into one of two paradigms, bottom-up or top-down. Microelectronic systems typically rely on integrated device platforms, where each device and component thereof can be individually addressed. This requirement for precise addressability places significant demands on the mode of fabrication, specifically with regard to device definition, placement and density, which have typically been strengths of top-down fabrication processes. However, in recent years advances in bottom-up fabrication processes have opened up the possibility of a synergy between bottom-up and top-down processes to achieve the benefits of both. This review article highlights the important considerations required for the continued advancement of semiconductor nanowire fabrication with a focus on the application of semiconductor nanowire fabrication for next-generation fieldeffect transistor devices. Figure 9 shows an SEM image of arrays of verti- 24cal Si nanowires produced using an EBL process.

Single-phase multiferroic materials are of considerable interest for future memory and sensing applications. Thin films of Aurivillius phase Bi7Ti3Fe3O21 and Bi6Ti2.8Fe1.52Mn0.68O18 (possessing six and five perovskite units per half-cell, respectively) have been prepared by chemical solution deposition on c-plane sapphire. Superconducting quantum interference device magnetometry reveal Bi7Ti3Fe3O21 to be antiferromagnetic (TN = 190 K) and weakly ferromagnetic below 35 K, however, Bi6Ti2.8Fe1.52Mn0.68O18 gives a distinct room-temperature in-plane ferromagnetic signature (Ms = 0.74 emu/g, μ0Hc =7 mT). Microstructural analysis, coupled with the use of a statistical analysis of the data, allows us to conclude that ferromagnetism does not originate from second phase inclusions, with a confidence level of 99.5%. Piezoresponse force microscopy (PFM) demonstrates room-temperature ferroelectricity in both films, whereas PFM observations on Bi6Ti2.8Fe1.52Mn0.68O18 show Aurivillius grains undergo ferroelectric domain polarization switching induced by an applied magnetic field. Here, we show for the first time that Bi6Ti2.8Fe1.52Mn0.68O18 thin films are both ferroelectric and ferromagnetic and, demonstrate magnetic field-induced switching of ferroelectric polarization in individual Aurivillius phase grains at room temperature

Periodic mesoporous materials have attracted considerable attention during the last decade because of their promising applications as catalyst supports and nanoreactors, or as hosts for nanostructured materials with appealing optoelectronic properties. [1,2] Many of these applications will benefit from arrangements of preferentially aligned, ordered arrays of certain mesostructures. The evaporation-induced self-assembly (EISA) method has been established as an efficient process for the preparation of thin films with mono-oriented mesostructured domains. [3,4] However, the most frequently obtained films display hexagonally ordered channels that are aligned parallel to the surface of the substrate. [5] Recently, the synthesis of mesoporous materials within the regular, larger channels of anodic alumina membranes (AAMs) has been explored, with the aim of attaining greater control over the morphology of the mesoporous system.[6] A first approach, through a sol-gel synthesis route using the triblock copolymer poly(ethylene oxide) 100 -b-poly(propylene oxide) 65 -b-poly(ethylene oxide) 100 (PEO 100 PPO 65 PEO 100 or Pluronic F-127) as a structure-directing agent, resulted in 2D hexagonal mesostructures with two different orientations that were found to coexist at different ratios depending on the concentration of the surfactant. [7] In one case, the long axes of the mesopores were aligned with the long axes of the AAM channels (columnar orientation). In another case, a circular orientation of the mesostructure was observed. Similar (freestanding) unusual mesophase structures are known to exist in cetyltrimethylammonium bromide (CTAB)-templated materials prepared by solvothermal methods and have been named "circulites" or circular crystals. [8,9] The efficient EISA method can also be used to prepare AAM mesoporous composite materials by applying coating solutions that are typically used for the deposition of mesoporous silica films. When using cationic CTAB as a template, partially ordered mesoporous materials with aligned, columnar mesopores only in the vicinity of the alumina walls were obtained that showed promising behavior as molecular separators.[10] Use of the triblock copolymer PEO 20 PPO 70 PEO 20 (Pluronic123 or P123) as a template resulted in striking mesostructures with concentric or helical mesopores and single chains of spherical mesopores, depending on the confinement conditions imposed by alumina nanochannels with diameters of less than 100 nm. [11] In contrast, columnar mesopores were reported when the same template (P123) was used in the sol-gel approach in larger Anopore channels.[12] However, when a slightly different protocol at the same surfactant/silica ratio was used in the solgel synthesis route, hexagonal mesophases with mixed orientations resulted.[13] The presence of water vapor in the ageing process was investigated in a related study using the P123 template. [14,15] In this case, the circular orientation was favored over the columnar one at higher water pressure; this selectivity was attrib...

Semiconducting nanowires (NWs) are important "building blocks" for potential electrical and electromechanical devices. Here, we report on the mechanical properties of supercritical fluid-grown Ge NWs with radii between 20 and 80 nm. An analysis of the bending and tensile stresses during deformation and failure reveals that while the NWs have a Young's modulus comparable to the bulk value, they have an ultimate strength of 15 GPa, which is the maximum theoretical strength of these materials. This exceptional strength is the highest reported for any conventional semiconductor material and demonstrates that these NWs are without defect or flaws that compromise the mechanical properties.

The development of semiconductor nanowires has recently been the focus of extensive research as these structures may play an important role in the next generation of nanoscale devices. Using semiconductor nanowires as building blocks, a number of high performance electronic devices have been fabricated. In this review, we discuss synthetic methodologies and electrical characteristics of Si, Ge, and Ge/Si core/shell nanowires. In particular the fabrication and electrical properties of a variety of nanowire-based field effect transistors (FETs) are discussed. Although the bottom-up approach has the potential to go far beyond the limits of top-down technology, new techniques need to be developed to realize precise control of structural parameters, such as size uniformity, growth direction, and dopant distribution within nanowires to produce nanowire-based electronics on a large scale.

A two-terminal bistable device, having both ON and OFF regimes, has been demonstrated with Ge nanowires using an in situ TEM-STM technique. The function of the device is based on delicately balancing electrostatic, elastic, and adhesion forces between the nanowires and the contacts, which can be controlled by the applied voltage. The operation and failure conditions of the bistable device were investigated, i.e. the influence of nanowire diameter, the surface oxide layer on the nanowires and the current density. During ON/OFF cycles the Ge nanowires were observed to be more stable than carbon nanotubes, working at similar conditions, due to the higher mechanical stability of the nanowires. The higher resistivity of Ge nanowires, compared to carbon nanotubes, provides potential application of these 1D nanostructures in high-voltage devices.

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